1. Technical Field
Embodiments of the present invention relate to a liquid ejecting apparatus such as an ink jet recording apparatus, and a control method for controlling the liquid ejecting apparatus. More particularly, embodiments of the invention relate to a liquid ejecting apparatus which applies a driving signal to a piezoelectric element so as to drive the piezoelectric element, thereby ejecting a liquid from nozzles, and a control method for controlling the liquid ejecting apparatus.
2. Related Art
A liquid ejecting apparatus is an apparatus that includes a liquid ejecting head and that ejects various liquids from the liquid ejecting head. Examples of the liquid ejecting apparatus include, for example, an image recording apparatus such as an ink jet printer or an ink jet plotter. A liquid ejecting apparatus has been recently applied to various manufacturing apparatuses by utilizing a feature in which a very small amount of liquid can be accurately landed on a predetermined spot. For example, the liquid ejecting apparatus may be applied to or included in a display manufacturing apparatus which manufactures a color filter of a liquid crystal display or the like, an electrode forming apparatus which forms the electrodes of an organic electroluminescence (EL) display or a surface emitting display (FED), and a chip manufacturing apparatus which manufactures a bio chip (biochemical element). In addition, a recording head for the image recording apparatus ejects liquid ink, and a color material ejecting head for the display manufacturing apparatus ejects a solution of each color material of red (R), green (G), and blue (B). Further, an electrode material ejecting head for the electrode forming apparatus ejects a liquid electrode material, and a bioorganic compound ejecting head for the chip manufacturing apparatus ejects a solution of bioorganic compounds.
In these liquid ejecting apparatus, the nozzles are exposed to air during the ejection of the liquid or during a recording operation. The liquid includes a solvent component that easily evaporates through the nozzles. However, if the solvent component has evaporated, there is a concern that the liquid near the nozzles may thicken and that the ejection of the liquid droplets may thus be hindered. Various countermeasures have been taken in order to reduce the thickening of the liquid. For example, in the above-described ink jet printer (hereinafter, simply referred to as a printer), the nozzle surfaces are enclosed by a cap member so that solvent evaporation from the nozzles is minimized when the recording head is in a standby state in which the recording head does not perform ejection or when a recording operation is not being performed.
In addition, a flushing operation, that is, an idle ejection (throwing-away-shot) operation of ink droplets is performed whenever a recording operation is performed for a predetermined time. Thickened ink is discharged from the recording head during the flushing operation.
Further, during execution of a printing process (a liquid ejecting process executed by receiving printing data and a printing command), in a nozzle which does not eject ink, a vibration driving pulse is applied to a pressure generator (for example, a piezoelectric vibrator) corresponding to the nozzle. A meniscus of the nozzle or ink in a pressure chamber communicating with the nozzle that does not eject ink is vibrated to an extent in which the ink in the pressure chamber is not ejected. In other words, the meniscus is slightly vibrated so as to allow the ink to be stirred without actually ejecting any of the ink from the nozzle. This prevents the ink from thickening. Furthermore, this slight vibration operation (e.g., vibration driving pulse) is also performed during the printing process when the recording head is moved to a region (non-recording region) which deviates from or is separated from a region (recording region) where the ink is ejected onto a recording medium (an ink landing target) such as recording paper (refer to JP-A-2003-039701).
Hereinafter, as appropriate, a vibration operation which is performed during a period when the recording head ejects the ink in the recording region in the printing process is referred to as “printing slight vibration”, and a slight vibration operation which is performed during a period when the recording head is located at the non-printing region and does not eject the ink in the printing process is referred to as “non-printing slight vibration”.
In a general printer, a reference potential of a driving signal in a recording region is made to match a reference potential of a driving signal (a driving signal including a vibration driving pulse for performing a non-printing slight vibration) in a non-recording region. However, in this configuration, the reference potential may be continuously applied to a pressure generator even in the non-recording region. As a result, the power consumption of the printer increases. In contrast, if the driving signal is not applied to the pressure generator in the non-recording region (an applied potential is 0), a non-printing slight vibration is not performed and it is hard to prevent thickening of the ink. Therefore, there is a problem in that the transition from a state in which the applied potential is 0 to a state of execution and restarting of the printing (execution of ejection of ink) is not smoothly performed. A time lag is necessary until a state occurs in which the ink can be ejected.
In addition, these problems occur not only the ink jet recording apparatuses in which recording heads which eject ink but also other liquid ejecting apparatuses which eject a liquid from nozzles by causing a pressure fluctuation in a liquid in a pressure chamber.